According to Diagnostic and Statistical Manual of Mental Disorders 4th ed. (American Psychiatric Association), obsessions are persistent ideas, thoughts, impulses or images that are experienced as intrusive and inappropriate and that cause marked anxiety or distress. They are intrusive because they interrupt the normal flow of thinking, dominating all other thoughts and the patient cannot control them. The patient struggles in vain to resist his obsessions, which can take up a great mount of time and energy, but usually the more resistant he/she is, the more strongly these thoughts come back. As opposed to psychotic disorders, they are contrary to the patient's very nature and he/she remains aware that these thoughts do not make sense and are a product of his/her mind. Most common obsessions include: thoughts about contamination, e.g. an excessive fear of dirt, germs, bodily fluids, dust, etc.; repeated doubts, e.g. about having done something or not, or about fearing to harm somebody; need to have things in a particular order, e.g. with perfect symmetry; aggressive or horrific impulses and images; and, sexual or pornographic images.
Together with these obsessions the patient may feel driven to compulsions, i.e., to repetitive behaviors or mental acts that are clearly excessive, in order to prevent some feared event or imagined danger becoming a reality. The most common forms of compulsive behavior are washing, cleaning, checking, requesting reassurance, hoarding, repeating, ordering, which can be time-consuming and interfere with the daily routine. The most common mental compulsions are counter-images, counting, rumination, and repeating prayers or words. A patient may suffer from one or more types of obsessions and compulsions at the same time. These obsessions and compulsions only become matters of clinical concern when their intensity and/or frequency cause marked distress, are time-consuming or significantly interfere with normal life, e.g. disrupting daily routines so much that working and concentrating correctly, taking part in social activities, or enjoying relationships with others becomes problematic.
Obsessive-Compulsive Disorder (hereinafter OCD), such as above defined, is a chronic psychiatric disorder with a worldwide lifetime prevalence rate of about 2.5%, according to P. Bebbington in Br. J. Psychiatry (1998) 173:2-6. The rate for OCD in first-degree relatives of OCD individuals is even above 10%. The rate for OCD is also higher for monozygotic twins than for dizygotic twins. The onset of OCD is usually earlier in males (between 6 and 15 years) than in females (between 20 and 29 years). Drugs that help OCD are classified as antidepressants, e.g. clomipramine (a serotonin-uptake inhibitor) and selective serotonin-uptake inhibitors (hereinafter SSRI) such as fluoxetine, fluvoxamine, sertraline and paroxetine. However, although about 60% of OCD patients have at least a moderate response to such medication, unfortunately at least 20% of OCD patients have no response at all to any of these drugs and fewer than 20% of those treated with such medication alone end up with no OCD symptoms. Moreover, the above-mentioned drugs have numerous side effects including nausea, drowsiness, insomnia, dry mouth and sexual dysfunction.
Clomipramine is even lethal in overdose. Another disadvantage of SSRIs is their ability to interact with other medications metabolized in the liver, thus either increasing side effects or inhibiting therapeutic benefits. Further, since the long-term effects of these drugs on a fetus are not yet clearly understood, giving such anti-obsessional medication to pregnant or breast-feeding women is usually avoided. According to most studies, a significant improvement in OCD symptoms is not noticeable until 6 to 10 weeks after starting SSRI treatment. Although some patients are able to discontinue medications after a six to twelve month period without relapsing, it is usually reasonable to stay on a full therapeutic dose for at least six months after OCD symptoms have been brought under control.
Some OCD patients may be helped with behavioral therapy, and often this kind of therapy is associated with the pharmacological treatment. Electro-Convulsive Therapy (ECT) is another alternative therapy, but only a few OCD patients improve thereafter.
In spite of the development of the above-mentioned therapies, a small, but significant proportion of OCD patients remain totally resistant to them. Furthermore, due to the side effects of the drugs and to the long-term treatment needed to ascertain the reality of symptom relief, some patients are discouraged because of the delay in improvement while side effects appear first and therefore tend to discontinue treatment at an early stage. A few of these patients, who are extremely ill and severely incapacitated, are candidates for neuro-surgical treatment.
Surgery for mental disorders is still a controversial issue partly due to the lack of randomized and double-blind controlled studies. However, neurosurgeons have been at least partially successful in treating chronic anxiety disorders by creating surgical lesions at specific locations in the neural circuitry of the brain that controls anxiety. For instance, there are numerous clinical reports substantiating that small and precisely placed lesions produced with stereotactic neurosurgical technique in specific regions of the brain (the anterior limbs of the internal capsules, the cingulum and the medial frontal subcaudate white matter) may ameliorate chronic and incapacitating OCD symptoms, as disclosed e.g. by Cosyns et al. in Adv. tech. Stand. Neurosurg. (1994) 21:239-279 and Lippitz et al. in Acta Neuroch. Suppl. (1997) 68:61-63. For the most part, these surgical procedures result in a destruction of the fiber pathways connecting various regions of the nervous system included in the list given above. Such a surgical treatment carries a low risk of complications and side effects but an obvious drawback is the irreversibility of a permanent lesion produced in the brain as documented by Stagno et al. in The Journal of clinical ethics (1994) 5(3):217-223 and by E. Hundert in The Journal of clinical ethics (1994) 5(3):264-266.
U.S. Pat. No. 6,128,537 “Techniques For Treating Anxiety By Brain Stimulation And Drug Infusion” by Rise issued Oct. 3, 2000 discloses using electrical stimulation in a nearly continuous manner to treat an anxiety disorder, e.g. by means of an implantable signal generator and an implantable electrode having a proximal end coupled to the signal generator and having a stimulation portion for electrically stimulating a predetermined stimulation site in the brain tissue. This patent discloses the following criteria for treatment of anxiety. Electrical stimulation of neural tissue may be implemented by providing pulses to two electrodes preferably having amplitudes of 0.1 to 20 volts, pulse widths varying from 0.02 to 1.5 milliseconds and repetition rates preferably varying from 2 to 2,500 Hz. An appropriate stimulation for use in connection with the anterior limb of the internal capsule is a high frequency stimulation, which aims at decreasing the neuronal activity in that portion of the brain. Enhanced results can be obtained by using a closed-loop system incorporating a sensor suitable for detecting symptoms of the disorder being treated, for instance a physiological signal related to heart rate, respiration rate, blood gases, galvanic skin response or muscle tension, the detected symptom being used to provide feedback to the patient to adjust stimulation parameters. The efficacy of treatment is enhanced if the neural tissue is stimulated while drugs such as GABA agonists are being administered by means of a pump implanted below the skin of the patient.
There is a need in the art for a method of treatment of OCD disorders which is safe and reversible and which provides the OCD patient with an effective relief from most OCD symptoms within a reasonable period of time while at the same time avoiding the various side effects of anti-depressant drugs such as clomipramine, SSRIs and GABA agonists.